// zdl:: 路标设置的题意，其实就按是可以使用二分答案的思想来解决问题


#include<iostream>

using namespace std;
int l, n, k;

const int N = 1e6 + 10;
int a[N];
bool check(int x)
{
    int cnt = 0;
    for (int i = 2; i <= n; i++)
    {
        int d = a[i] - a[i - 1];
        cnt += d / x;
        if (d % x == 0) cnt--;
    }
    return cnt <= k;
}
int main()
{

    cin >> l >> n >> k;
    for (int i = 1; i <= n; i++) cin >> a[i];
    int right = l, left = 1;
    while (left < right)
    {
        int mid = (right + left) / 2;
        if (check(mid)) right = mid;
        else left = mid + 1;
    }
    cout << left << endl;
    return 0;
}